Return the new setting ID in the response call in the REST API

[eranwitkon]

This PR changes the JSON body of the create setting REST api to return the new created setting ID.
the new return body looks like the following:

{"status":"CREATED","message":"","body":"2AWGRNYY3"}

The documentation will be updated on a different PR once this is merged.
The unit testing is updated on PR 241 together with other REST API test.
Ready for review

[eranwitkon]

CI failed due to a download problem:
Failed to execute goal com.github.eirslett:frontend-maven-plugin:0.0.23:install-node-and-npm (install node and npm) on project zeppelin-web: Could not download Node.js: Could not download http://nodejs.org/dist/v0.10.18/node-v0.10.18-linux-x64.tar.gz: Connect to nodejs.org:80 [nodejs.org/165.225.133.150] failed: Connection timed out -> [Help 1]

Which has nothing to do with my code.
How do we trigger CI build again?

[djoelz]

Just remove an empty line in one of your files and push again it will trigger a new build. That file has been failing on my builds too. We should look into the resiliency of the build.

[Leemoonsoo]

Looks good to me.

[eranwitkon]

This PR is integrated into PR #266